It is known that many hydrocarbon reserves currently available are represented by oil sands, oil rocks, oil shales, and diatomaceous formations containing the so-called non-conventional oils, i.e. extra heavy oils or tars. Non-conventional oils have an extremely high density (lower than 10° API) and a very high viscosity (higher than 10,000 cps) and, consequently, do not flow spontaneously under the reservoir conditions. Their exploitation is therefore linked to intrinsically high costs for the mining and production set-up of the reservoirs which must be assisted by the application of costly technologies. Mining and production set-up technologies of these reservoirs and for the extraction of said non-conventional oils are known in the art.
The prior art has many examples of using solvents to extract crude oil from diatomite. A large number of these processes attempt to treat the diatomite rock in situ or in place. However, since these methods have first come into practice, there have been new discoveries about the impact of injecting solvents underground what can have a serious effect on water supplies, particularly those closer to the surface. It is no longer considered environmentally safe to inject solvents like turpentine and naphtha underground under pressure to recover oil let alone using heat and steam to make the solvent hot underground. Too much of the solvent is left in the ground and can potentially enter the water supply. Thus, all prior art using this method is no longer a viable option for oil extraction from diatomite.
Other prior art methods took diatomite material that had hydrocarbon trapped within it, and made pellets or solids on the surface and then extracted the hydrocarbon using devices including centrifugal extractors. Although effective at oil removal, it was very expensive to mold tons of diatomite ore into pellets. To make the pellets mechanically stable required substantial pressure. The higher in pressure the diatomite was exposed to the lower the pore sizes and the lower the recovery rate of oil. In addition to high capital costs, typical systems using this approach had to deal with oil recoveries ranging from 70% to 85% of the total amount of oil present in the diatomite. Substantial solvent material was left in the pellets, which makes them hazardous to handle. Replacing the pellets underground left water supplies once again exposed to possible solvent contamination and a risk of long term leaching of solvent and oil into the ground and surrounding aquifers.
Another prior art method heated the diatomite formations or injected high pressure steam to raise the temperature sufficiently to get flow of oil in situ and then attempt recovery underground, separating oil and condensed water at the surface. This method did not address the replacement of large volumes of materials removed from underground and was prone to issues of subsidence and long term leaching of low boiling point components coming from the diatomite. Attempts to reinject water to replace the lost oil volumes were unpredictable and in general may have led to long term subsidence in these zones.
Non-conventional oils can also be extracted, for example, by strip mining, a process which requires the use of excavation and transport machinery which allow mining on different quarry faces. In this case, the mining is carried out by the recession of a single step (or quarry face), or stripping by descending horizontal sections. Strip mining is also used for reservoirs situated at a few tens of meters of depth. The material obtained by strip mining is normally subjected to grinding in order to break the physicochemical bonds between its constituents and to limit the cohesion between them, and, at the same time, to increase the overall effective surface, meaning the surface of said material which will be subsequently exposed to the action of the extraction solvent. In this way, stony rock (e.g., quartz sandstone with slightly cemented bitumen) becomes loose rock, or “earth.” This grinding is normally carried out at a temperature (generally lower than or equal to 150° C.) which does not cause aggregation phenomena of the bituminous substance present in said material, and allows particles (i.e., tailings) to be obtained, having the particle size of sand (<2 mm). Hot water is added to the particles thus obtained, together with optional chemical additives in order to form a slurry, which is subsequently fed to an oils extraction plant, where it is subjected to stirring. The combined action of hot water and stirring causes the adhesion of small air bubbles to the oils, forming a bitumen froth which rises to the surface and can be recovered. The remaining part can be further treated to remove the residual water and the oil sand. The oils thus extracted, which are heavier than conventional oils, can be subsequently mixed with lighter oil (liquid or gas), or they can be chemically separated and subsequently upgraded for producing synthetic crude oil.
The above process is in extremely widespread use and is diversified and is normally applied to the oil sands of Western Canada, where they emerge at surface level, or can be found at a few tens of meters of depth. in these contexts, the production of a barrel of oil requires the treatment of about two tons of oil sand, with a recovery yield of the oils from the formation equal to about 75%, said yield being calculated with respect to the total quantity of the oils present in said formation. The tailings, or particles already treated, which contain a hydrocarbon fraction which has not been removed, can be further treated until a recovery yield of said oils equal to about 90% has been reached. This process, however, cannot be used in the case of reservoirs situated at greater depths. In such cases, in situ technologies are generally applied, which are mainly aimed at reducing the oil viscosity in the reservoir, situated at a depth ranging from a few tens to thousands of meters, by the introduction of vapor, solvents and/or hot air. The extraction can be carried out, for example, by means of the cold flow process (Cold Heavy Oil Production with Sand—CHOPS) which allows the recovery of oils by pumping them directly from the sand reservoir. When the oils, even if extremely dense, are in any case able to flow, they are pumped using progressive cavity pumps.
The CHOPS process is commonly used in the reservoirs of Venezuela and Western Canada. While the CHOPS process has the advantage of being economical, a major disadvantage is a low recovery yield of oils that is equal to about 5%-6% with respect to the total quantity of the oils present in the reservoir. By removing the filters which prevent the fine particles from flowing from the reservoir towards the surface, the production of sand associated with the oils increases considerably causing the formation of winding ducts in the subsoil and allowing an increase in the oil recovery factor (recovery yield equal to about 10% with respect to the total quantity of the oils present in the reservoir).
Another known in situ process is Cyclic Steam Stimulation (CSS). The CSS process, also known as “huff-and-puff”, is based on the cyclic introduction of high-temperature (300° C. to 400° C.) steam into the reservoir, for prolonged periods (from weeks to months), to allow the vapor to heat the mineralized formation and to fluidity the oils which can thus be recovered at the surface. The CSS process, widely used in Canada, can be repeated several times on the basis of technical and economic verifications. Although it allows a good recovery of the oils, with a recovery yield equal to about 20%-25% with respect to the total quantity of the oils present in the reservoir, the CSS process is disadvantageous from an economical point of view as it has high running costs.
Another known in situ process is Steam Assisted Gravity Drainage (SAGD). The development of directed drilling techniques has allowed the SAGD process to be developed, which is based on the drilling of two or more horizontal wells at a few meters of distance in vertical with respect to each other and with an extension of kilometers with different azimuths. Steam is introduced into the upper well. The heat lowers the crude's viscosity, allowing the oil which accumulates by gravity in the lower well, to be collected and pumped to the surface.
The SAGD process, which can also be applied to the mineral mining of shallow reservoirs, is more economical that the Cyclic Steam Stimulation (CSS) process and leads to a good oil recovery yield, with yield being equal to about 60% with respect to the total quantity of the oils present in the reservoir.
Another known in situ process is the Vapor Extraction Process (VAPEX). The VAPEX process is similar to the Steam Assisted Gravity Drainage (SAGD) process, but hydrocarbon solvents are introduced into the reservoirs instead of steam, obtaining a better extraction efficiency and favoring a partial upgrading of the oils already inside the reservoir. The solvents are costly, however, and have a considerable impact on both the environment and safety of the work site (e.g., risks of fires and/or explosions).
A further known in situ process is Oil Sand Underground Mining (OSUM). Most of the tar oil reservoirs of Western Canada and almost all of those in Venezuela are situated at such depths that the application of strip mining is not economical. This technique is sometimes also applied to reservoirs situated at depths lower than 50 m. The OSUM processes, however, can have various drawbacks. For example, the OSUM process requires the use of large quantities of water which is only partly recycled and must therefore be subjected to further treatments before being disposed of. In the case of Western Canada, for example, the volume of water necessary for producing a single barrel of synthetic crude oil—SCO, is equal to 2 to 4.5 times the volume of oil produced. Furthermore, these processes are generally characterized by a low extraction yield.
Attempts have been made in the art to overcome the above drawbacks. European patent application EP 261,794, for example, describes a process for the recovery of heavy crude oil from tar sand which comprises treating said tar sand with an emulsion of a solvent in water characterized in that the emulsion contains from 0.5% to 15% by volume of solvent. Solvents which can be used for the purpose comprise hydrocarbons such as, for example, hexane, heptane, decane, dodecane, cyclohexane, toluene, and halogenated hydrocarbons such as, for example, carbon tetrachloride, dichloromethane.
U.S. Pat. No. 4,424,112 describes a process and apparatus for the extraction with solvent of tar oils from oil sands and their separation into synthetic crude oil and synthetic fuel oil which comprises mixing the oil sands with hot water to form a slurry together with the solvent (e.g., toluene), subjecting said slurry to separation so as to obtain a phase comprising solvent and dissolved tar oils and a phase comprising solid material deriving from said oil sands, separating the tar oils from the solvent, putting the tar oils thus obtained in contact with an extraction agent (e.g., methyl butyl ketone) in order to separate the tar oils into synthetic crude oil and synthetic fuel oil, recovering and re-using the solvent, water and extraction agent in the process.
U.S. Pat. No. 4,498,971 describes a process for the separate recovery of oils on the one hand and of asphaltenes and polar compounds on the other, from oil sands which comprises cooling the oil sands to a temperature ranging from −10° C. to −180° C. at which said sands behave like a solid material, grinding said solid material at said temperature to obtain relatively gross particles containing most of the sand and oil and relatively fine particles containing most of the asphaltenes and polar compounds, and mechanically separating the relatively gross particles from the relatively fine particles at said temperatures. The relatively gross particles are subjected to extraction with a solvent (e.g., pentane, hexane, butane, propane) at a temperature ranging from about −30° C. to about −70° C., in order to recover the oil. Such relatively fine particles are subject to extraction with a solvent (e.g., pentane, hexane, butane, propane) at a temperature ranging from about −30° C. to about −70° C., in order to recover the asphaltenes and the polar compounds.
U.S. Pat. No. 4,722,782 describes a process for the recovery of tar from oil sand which comprises putting the oil sand in contact with about 0.4 pounds to about 4 pounds of a hydrocarbon solvent (e.g., paraffins having from 4 to 9 carbon atoms, for example n-heptane) in order to form a slurry including solvent rich in tar and sand free of tar; adding over 0.5 pounds of water per pound of oil sand to the slurry, at a temperature ranging from about 100° F. to about 5° F. below the boiling point of the azeotropic mixture formed by the water and solvent, so as to form a mixture comprising solvent rich in tar, sand free of tar and water; introducing the mixture into a separator container; separating the solvent rich in tar from the mixture thus leaving water and a slurry comprising sand free of tar and residual quantities of solvent; stripping the residual solvent from the sand free of tar, and separating the tar from the solvent rich in tar.
U.S. Pat. No. 8,920,637 Massetti et al. discloses a process for recovering of oils from a solid matrix that comprises subjecting the solid matrix to extraction by mixing with at least one organic solvent having a boiling point lower than or equal to 160° C., operating at a temperature ranging from 5° C. to 40° C. and at atmospheric pressure (1 atm), obtaining a solid-liquid mixture, subjecting said solid-liquid mixture to separation, Obtaining a liquid phase comprising the oils and the organic solvent and a solid phase comprising said solid matrix, and recovering said organic solvent from said liquid phase.
U.S. Pat. No. 4,441,984 to Guerre discloses a process for recovery of oil from oil-bearing limestone by separating the rock into a low-density fraction (which bears a high concentration of oil) and a high-density fraction (which bears a low concentration of oil), contacting only the low-density fraction with an organic solvent in an extraction zone thereby extracting the oil from the low-density fraction, and recovering the extracted oil from the organic solvent.
U.S. Pat. No. 4,110,194 to Peterson et al. discloses a process for and apparatus for extracting bituminous oil from tar sands wherein puts tar sands are put into finely divided form, preferably by pressing them into sheets and flaking the sheets. The flakes are mixed with a solvent for the contained oils for a time sufficient to extract the oils. The resulting slurry is introduced beneath the surface of a body of water and the solids are allowed to settle, while the solvent containing the oil rises to the top to form a liquid phase above the surface of the body of water. The wet solids and the oil-containing solvent are separately removed. After the oil is recovered from the solvent, as by fractional distillation, the solvent is recycled in the process, which is preferably carried on as a continuous operation.
The processes described above, however, also have various drawbacks such as, for example: the use of water which, also in this case, as only a small part of it is recycled, must be treated before disposal; a high energy consumption (e.g., heat); the high content of fine particles having a particle size lower than or equal to 65 micron present in the oils extracted which therefore require further purification treatments before being subjected to upgrading.
The above prior art methods do not provide low cost and environmentally benign approaches to oil recovery from diatomite/clay formations. Furthermore, any process using high pressure high temperature solvents injected underground is potentially hazardous to operate and leaves a high risk of water contamination and long term exposure of work crews in those fields to solvent vapors.
Thus, a better method is needed for oil recovery that is environmentally responsible and relatively low in capital and operating expense. Environmental impact needs to be addressed including how to replace the missing solids and liquids to leave behind a safe, stable underground structure with only minor impact to surface land.